Aerosols or particulate are present in many workplaces, and occupational hygienists around the world have different approaches for managing and controlling risks and exposures related to these hazards. For example, in the United States, AIHA proposes the ARECC framework, which calls for occupational hygienists to anticipate and recognize hazards, evaluate exposures, and control and confirm protection from risks. Guidelines and regulations issued by U.S. federal agencies like NIOSH, OSHA, and MSHA address specific aerosols from diesel particulate matter to overall respirable dust, and from crystalline silica to carbon nanotubes and other products found in additive manufacturing. In Europe, the general obligation for employers to provide safe workplaces for their employees is described in European Directive 89/391/EEC. In general, the European occupational safety and health framework comprises six steps: preparation, risk analysis, risk assessment, taking measures, reviewing and updating the risk management process, and documenting the process. This framework may differ slightly across Europe and is commonly referred to as the risk inventory and evaluation process. In other countries, like Australia, more emphasis is placed on mitigation and control strategies for aerosols and other hazards.

No matter their approach, occupational hygienists around the world recognize the role of exposure and hazard monitoring in generating valuable data in each step of these frameworks. Aerosol or particulate monitoring is used to quantify the personal exposures of workers or the hazardous concentration levels in the workplace. The methodologies used to monitor occupational aerosols have evolved in the past several decades—from collecting aerosol particles in bulky impingers and then counting them with optical microscopes, to pre-programmable personal sampling pumps and samplers as well as accurate and selective analytical methods including gravimetric analysis, spectroscopy, thermo-optical analysis, diffractometry, and mass spectroscopy.

During this evolution, the core of the methodologies remained the same: the collection of a sample for a period of time (a full or partial work shift, for example) with the help of a sampler and media, followed by laboratory analysis using standardized analytical methods. The sampler can differ depending on the task at hand—for instance, different situations may call for the sampling of total, inhalable, respirable, or submicron particles. And a wide range of specific exposures, including welding fumes, diesel particulate matter, elongated mineral particles, generic respirable aerosols, crystalline silica, and single metal elements can be analyzed and quantified. But laboratory analysis focuses on generating information related to the time-weighted average (TWA) concentration levels of the particulates of interest, which become the only information used for any steps taken by occupational hygienists using the previously mentioned frameworks.

On these pages, we will explore the strengths and limitations of established time-integrated monitoring methodologies for aerosols, discuss how real-time particulate monitors (RTPM) may add to these methodologies, and highlight barriers or roadblocks to the adoption of RTPM. We will also propose a call for guidelines toward the systematic adoption or operationalization of RTPM in occupational hygiene.

STRENGTHS AND LIMITATIONS OF TWA SAMPLING Three factors contribute to the use of TWA as the most common type of data used in relation to particulate, even though it is well known that the concentration of and exposure to this hazard is highly variable in time in most cases.

The chronic nature of many health effects associated with prolonged exposure to most particulates is the first factor. The assumption here is that the risk is not associated with an exposure during a very short period of time, but rather the average (shift) exposure or the cumulative exposure over multiple months or years. From a feasibility perspective, the length of a single shift, which may be assessed once or multiple times, is the longest duration of time for averaging the concentration of particulate. Although many effects of particulate exposures are chronic in nature, it is possible that acute health effects or exacerbations associated with peak exposures have not been recognized due to the lack of methods to monitor them.

This assumption informs the second factor, which is that occupational exposure limits for particulate found in standards and regulations are set as TWA. Most OELs account for exposures that occur for eight hours per day, five days per week for 40 years or similar. The fact that OELs for respirable dust and other associated aerosols like silica are set up as TWA of mass concentration is an important factor that explains why professionals measure the exposure levels of workers in the same way. One of the goals of any health and safety program is to assess compliance with OELs, and for this reason alignment in terms of measurement is critical. Simply put, an occupational hygienist measures exposures in the way that the workplace will be assessed for compliance. While this makes sense, it does not mean this is the only way occupational hygienists should assess and measure exposure in the workplace.

The third factor has to do with the level of accuracy and performance of available analytical methods and overall monitoring approaches used for measuring the exposure of workers to any particulate and associated particles. As a result of the other two factors, each element of the sampling and analysis process has been developed, assessed, and constantly revised by national and international standardization organizations. This is the case for the performance of respirable dust samplers and sampling pumps to assure the collection of representative samples, and for the performance of laboratories to assure the accuracy, precision, and inter-laboratory results variability for the analytical methods they employ. OH professionals have high confidence in the average exposure concentration data obtained from the samples they collect. This confidence is critical when it comes to making decisions associated with the results. If the quality of the data is so good, why change the approach and use methods that have not been standardized and that may be less accurate?

It is important to recognize that TWA methodologies for particulates have intrinsic limitations. For example, TWA methodologies cannot provide any granularity regarding changes in concentration or personal exposure during the shift or sampling time. There is also no proper way to identify, recognize, and evaluate what specific task, activity, or combination of activities are the main contributors to the TWA value, which can hamper effective control. And because of the cost and complexity associated with the generation of each TWA datapoint, occupational hygienists collect relatively few samples to be analyzed. Fewer datapoints can make it more challenging to define similar exposure groups. Finally, the time it takes to complete the cycle of sample collection, laboratory analysis, and results generation can range from several days to several weeks depending on the aerosol of interest and the region of the world. This can delay timely action and effective risk communication.

BARRIERS TO THE SYSTEMATIC ADOPTION OF RTPM Direct-reading methodologies for aerosols and particulates are available and include RTPM. Articles published in 2021 by the Annals of Work Exposures and Health and in 2022 by the Journal of Occupational and Environmental Hygiene (see the resources section on page 22) help inform practitioners about occupational exposure modeling and time-resolved sensor data as well as direct-reading instruments for aerosols. These technologies could address the shortcomings of TWA sampling with their ability to generate data with higher resolution than TWA and immediate feedback to the workplace and even to workers. RTPM can also help increase the number of datapoints in time.

Different types of RTPM that are currently available or are in development will provide versatility and flexibility not possible with TWA methodologies. RTPM devices differ in range, cost, quality, characteristics such as internet connectivity, and deployment. Such variety is beneficial but can also be confusing. RTPM—and in general any direct-reading instrument or sensor—should be used in combination with, not as an alternative to, conventional TWA methodologies within the existing OH frameworks. (See the Synergist article “The Challenge for Industrial Hygiene 4.0” for additional discussion of real-time monitoring in occupational environments.) Practitioners can visualize these methodologies as part of a toolbox that can be used by the OH professional to address aerosols or particulates. Each step of an OH framework comprises different activities, such as physical and data analysis processes. Each activity can benefit from a different selection of technologies and methodologies from the toolbox and a different approach toward data quality and adoption. For some applications, the use of RTPM might be only qualitative, and in other situations, RTPM may provide quantitative metrics that are completely different from metrics derived from TWA methodologies.

Despite the potential of RTPM and the “toolbox approach,” barriers to the systematic adoption of these technologies remain. For example, the quality of data generated by RTPM is a concern—and rightly so since most technologies adopt surrogate measurements and complicated algorithms to provide an indicative estimation for the concentration levels. The landscape of commercially available technologies is extensive, and each technology has its peculiarities. Communication between vendors and users presents another potential challenge in that it is not always effective and productive: for instance, OH professionals are supposed to be knowledgeable in aerosol science and technologies so they can navigate in-person and virtual exhibitions and expositions to select the right technology and use it properly. Since RTPM technologies do not require laboratory analysis, the OH professional becomes the only party responsible for the actual performance of the device. This is a substantial shift in responsibilities, even when the quality of the data is well understood. Even so, OH professionals already have similar experience related to other hazards like noise and gas/vapor for which direct-reading instruments are more established.

Another barrier to the adoption of RTPM is technological in nature and relates to usability. The adoption of any technology, including RTPM, is a burden for the OH professional and workplace. There is always a learning curve—sometimes a steep one—to implement new technology. Setup, proper calibration, and daily and periodic maintenance are aspects to consider before making a technology change. Potential adopters of RTPM must also navigate the transfer of data from the device to a database, the synchronization of datasets, the standardization of the information, and the interpretation of the data. These steps lead to the transformation of data into information and knowledge—the true benefit of adopting RTPM—but they can be burdensome. Thanks to innovative data transfer methodologies, effective dashboards, and other visualization means, this roadblock is becoming gradually more manageable.

It can also be difficult to fully understand the added value of RTPM in the context of OH activities and frameworks. While the general benefit of using RTPM for monitoring aerosols or particulate in the workplace is known and is the subject of presentations at conferences, there remains a lack of guidelines for implementation of RTPM and for operationalization—particularly for specific applications. Academic and professional development courses on real-time sensors and RTPM tend to focus primarily on technical aspects and validity compared to conventional TWA methods, rather than on discussion of the opportunities related to RTPM use. Until the added value of RTPM is thoroughly investigated and widely understood, use of the technology will likely be occasional and nonsystematic. This could be a missed opportunity.

CALL FOR GUIDELINES We believe it’s time for the occupational hygiene community to discuss and develop guidelines to enable a shift into a new era in which RTPM are systematically adopted in OH frameworks. These guidelines should recognize and address the barriers described in this article. The performance of these technologies must be better disclosed by manufacturers and understood by OH professionals, and in the future RTPM must be regulated by standards. The technology’s usability will improve as it has in the past decades. But, most importantly, OH practitioners and pracademics (practitioner-academics) have the responsibility and opportunity to explore, experience, and report the added value associated with RTPM.

The term “guidelines” can be explained in many ways. For the purposes of this article, guidelines are not necessarily rules or laws but are more like recommendations and logical steps for the appropriate and knowledgeable use of technologies. The term “playbook” is sometimes used instead of “guidelines.” A playbook imagines scenarios of a certain practice before they happen. Guidelines are often presented as a white paper to indicate the nonprescribed nature of the information they contain. Consider the recently published AIHA white paper “Establishing a Process for the Setting of Real-Time Detection System Alarms” (PDF): it is a good example of a guideline for the systematic adoption of real-time systems, including RTPM, because it addresses the barriers to and value added by the technologies together with discussion of the limitations of quality in the data. The white paper can ultimately be used for guidance in setting up alarms and alerts.

The creation of RTPM guidelines must be a participatory process, and OH practitioners should actively take part. While standardization bodies can help tackle some roadblocks, their process for developing guidelines or standards is slow and meticulous. Standardization bodies do not release standards until they are deemed perfect. We believe that this approach is the opposite of what is currently needed: guidelines that are timely and constantly changing. The advancement of RTPM technology is too fast for standards to keep up, and practitioners are already using these technologies. Each application might require a specific standard and more time. The participatory process for the creation of RTPM guidelines should include working groups, task forces, and communities of practice at the national and international levels to be as inclusive as possible and to consider a variety of perspectives. Some of these groups already exist, but others must be created.

During the development of guidelines for RTPM, different stakeholders should have the opportunity to discuss varying opinions and experiences. It’s important that everyone involved in the process be aware that RTPM technologies are misused at a not-insignificant rate and that information from the manufacturers is not always clear. (An example of misuse is simply an implementation that requires more work and digestion.) While OH practitioners should embrace a “right sensors used right” mindset (as explained by NIOSH) as best they can and as soon as possible, the implementation of RTPM technology may not be perfect at first. It’s also important to continue engaging with companies and other entities that provide information about RTPM, even if the information could be improved. There is no future for the adoption of RTPM and the evolution of OH practice without providers or creators of technologies such as sensors, software, and information technology infrastructure. Imperfect implementation and gaps in information are to be expected as technologies like sensors and RTPM advance.

These new guidelines should separately or synergistically address the barriers to the systematic adoption of RTPM. Discussion of examples, experiences, and successes and failures in terms of added value will help identify metrics to be used to evaluate the quality of data generated by RTPM and for related standards.

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